This invention relates to Schottky barrier contacts, and more particularly, to techniques for modifying the electronic barriers of such contacts.
A Schottky barrier contact is a metal contact formed on a semiconductor wafer so as to establish a rectifying electronic barrier or junction. The barrier is created because of differences in work function of the metal and semiconductor and is conventionally characterized by a barrier height measured in electron-volts. An internally-generated electric field extends into the semiconductor from the metal and establishes a depletion region, even in the absence of any external voltage.
As is well known, Schottky barrier diodes are widely used as high-speed switching diodes, microwave mixer diodes, and voltage clamping diodes. Schottky barrier contacts are commonly used in integrated circuits in which the semiconductor substrate includes numerous other components. A specialized microwave device using Schottky barriers is the BARITT device described in the patent to D. J. Coleman et al. 3,625,514, issued June 27, 1972 and assigned to Bell Telephone Laboratories, Incorporated.
One common Schottky barrier contact comprises platinum bonded to silicon which forms a barrier having a height of about 0.87 electron-volts. Since the height of the Schottky barrier is determined by the combination of metal and semiconductor used, it is difficult to control the height of the barrier or otherwise to control the conditions under which current is transmitted across the barrier. Thus, platinum-silicon Schottky barrier diodes require a forward-bias turn-on voltage in excess of 0.6 volts. It has long been recognized that if the barrier could be lowered or otherwise modified, the forward turn-on voltage could be reduced and greater flexibility in device design could be obtained. Efforts have therefore been made to modify the barrier by etching the contact surface of the semiconductor, deforming the contact surface, and using other techniques. Various combinations of metal and semiconductor metals have been used, but all of these expedients typically require significant sacrifices of desirable electrical and mechanical characteristics and have not been used extensively.